Should Power Lines be Underground?

After storms cause extensive damage to overhead electrical lines, it’s natural to wonder if it would be better to bury lines underground to protect them from wind, vegetation, debris or ice. Entergy is not opposed to all undergrounding projects—in fact, power lines in some downtown business districts and many neighborhoods in our service area are already underground. However, customers should be aware of the pros and cons.

Underground has several noteworthy advantages • There’s the obvious aesthetic consideration. Except for an above-ground terminal here and there, they’re out of sight entirely. • They are less vulnerable to airborne elements like wind and ice. • In some areas, like downtown districts, they are often more practical than overhead lines.

• While overhead lines are exposed to damage from airborne debris, trees and public interference, outages typically take less time to restore than underground outages. • Underground lines are less susceptible to damage caused by wind, trees and ice, but face outages from trees collapsing on above-ground transformers and switch boxes or from tree-root sysUnderground costs more to tems uprooting buried cable when install and maintain, resulting in trees fall. increased electric rates • As underground cables ap• Several studies have shown proach the end of their life, failure rates increase signiﬁcantly, and that installing lines underground is expensive for customers and these failures are extremely difﬁtaxpayers, costing 10 times more cult to locate and repair. Besides having accumulated than overhead distribution or • While a neighborhood may be a great deal of experience of transmission lines. locally served by underground our own, this topic has been • Underground lines are much lines, all electric service eventuwidely studied. See page 2. more difﬁcult and expensive ally comes back above ground and to work on when problems connects to overhead service, eiarise. They require earth-moving equipment and ther in the neighborhood next door or further down specialized technicians. the street where overhead main lines and transmis• Installing underground is best done as an area sion lines move electricity from power plants and is being developed. This is less expensive than substations into our neighborhoods. Thus, exposure converting later from overhead to underground. of above-ground and overhead service to problems • Overhead systems are easier, thus less expensuch as weather or trees cannot fully be eliminated. sive, to upgrade, such as when a community grows In fact, after Hurricane Wilma struck South Florida and needs additional electricity capacity. in 2004, the media reported that 97 or 98 percent of • Several state regulatory agencies have found Florida Power & Light customers in Broward County that the cost of burying power lines is much more lost power, even though 54 percent of them were than the beneﬁt provided. served by underground lines. • Storm-related ﬂooding – particularly salt-water ﬂooding – can cause and prolong outages in unUnderground lines are not necessarily more reliable than overhead lines derground systems, and can shorten the life and increase the ongoing maintenance of the under• Typically, underground lines experience fewer outages. But when outages involving underground ground system. lines do happen, they typically last longer because underground lines are more difﬁcult than overhead lines to troubleshoot and repair.

Real-world Experience and Third-party Research on the Feasibility of Underground Power
• A 2006 study by the Edison Electric Institute found that burying overhead power lines costs approximately $1 million per mile, 10 times what it costs to install overhead lines. • A 2007 study by Entergy Texas, made at the request of the Public Utility Commission of Texas, reached a similar conclusion: construction of underground transmission lines is roughly 10 times more expensive than overhead construction. On a per mile basis, it costs $5 million to build an underground transmission line versus $500,000 for overhead construction. • Studies of statewide undergrounding proposals in North Carolina in 2002 and Florida in 2003 suggest that undergrounding distribution lines would require rate increases ranging from 80 percent to 125 percent. • A 2004 study by the Virginia Corporation Commission calculated the annual cost of a statewide undergrounding initiative at approximately $3,500 per customer. Based on the projected costs and beneﬁts for undergrounding much of its state’s electric system, the Virginia commission calculated that the beneﬁts would offset only about 38 percent of total costs and concluded that a comprehensive statewide effort to bury the state’s electric distribution system appears “unreasonable.”

• In 1998 Australian ofﬁcials completed what may be the most comprehensive research to date to quantify the beneﬁts and costs related to undergrounding. The Australian study reached a conclusion similar to the Virginia study and estimated that the beneﬁts of undergrounding would offset only about 11 percent of the costs. • A ﬁve-year survey (1998-2002) of underground and overhead reliability comparisons for North Carolina’s investor-owned electric utilities – Duke Energy, Progress Energy Carolinas and Dominion North Carolina Power – indicated that the frequency of outages on underground systems was 50 percent less than for overhead systems, but that the average duration of an underground outage was 58 percent longer than for an overhead outage. • A 2000 study by the Maryland Public Service Commission looked at the reliability of “comparable” overhead and underground feeders and concluded that the impact of undergrounding the lines was, at best, “unclear.” As underground cables approach their end of life, the Maryland report showed, failures increase signiﬁcantly and are extremely difﬁcult to locate and repair. Maryland utilities say their underground cables become unreliable after 15 to 20 years and reach their end of life after 25 to 35 years.

The North Carolina Experience
In early December 2002, a major ice storm blanketed much of North Carolina with up to one inch of ice, causing an unprecedented power outage to approximately two million electric utility customers. In the immediate aftermath of the storm, the public expressed considerable interest in burying all overhead power lines in the state. A special Natural Disaster Preparedness Task Force investigated the issue for the North Carolina Utilities Commission and unequivocally recommended against the step. The task force study “determined that replacing the existing overhead distribution lines of the (state’s investor-owned) utilities with underground lines would be prohibitively expensive. Such an undertaking would cost approximately $41 billion, nearly six times the net book value of the utilities’ current distribution assets, and would require approximately 25 years to complete. The ultimate impact of the capital costs alone on an average residential customer’s monthly electric bill would be an increase of more than 125 percent.” Rates would also be impacted by the higher operating and maintenance costs associated with direct-buried underground systems, particularly in urban areas, where underground conductors are four times more costly to maintain than overhead facilities, the task force found. “In addition to the impact on the cost of providing utility service, conversion to underground would impose costs on individual customers, municipalities, and other utilities,” it added. “While these costs have not been quantiﬁed, they could be signiﬁcant.” The report also determined that “underground facilities are not without their disadvantages. Although underground systems are more reliable than overhead systems under normal weather conditions, they are not impervious to damage, and the repair time for underground systems is almost 60 percent longer than for overhead systems when damage does occur. Consequently, the [Task Force] does not recommend that the utilities undertake the wholesale conversion of their overhead distribution systems to underground.”